How can email possibly be routed to the right place with no to: address?
I've seen this quite a few times now. I will receive an email at a domain that I manage (firstname.lastname@example.org) from an @yahoo.com account but the To header has an email at some entirely unrelated domain name! The DKIM signature contains the To header and they pass validation. How can this be?
Return-Path: <email@example.com> Received: from nm8.bullet.mail.ukl.yahoo.com (nm8.bullet.mail.ukl.yahoo.com [126.96.36.199]) by mx.example.com with SMTP; Mon, 19 Nov 2012 16:38:59 -0500 Received: from [188.8.131.52] by nm8.bullet.mail.ukl.yahoo.com with NNFMP; 19 Nov 2012 21:38:56 -0000 Received: from [184.108.40.206] by tm20.bullet.mail.ukl.yahoo.com with NNFMP; 19 Nov 2012 21:38:40 -0000 Received: from [127.0.0.1] by smtp113.mail.ukl.yahoo.com with NNFMP; 19 Nov 2012 21:38:40 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1353361120; bh=uCWr2zakkKwpxVn224ejIuEu24fxI7P+IKguxaa4T50=; h=X-Yahoo-Newman-Id:X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:Date:From:Subject:To:Content-Type:X-Mailer; b=O6...(shortened) X-Yahoo-Newman-Id: firstname.lastname@example.org X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: 7YH8p9Y...(shortened) Received: from uxprj (email@example.com with login) by smtp113.mail.ukl.yahoo.com with SMTP; 19 Nov 2012 13:38:40 -0800 PST Message-ID: <50AA5277.4653079B@smtp.mail.yahoo.com> Date: Mon, 19 Nov 2012 15:38:40 -0600 From: "firstname.lastname@example.org" <email@example.com> Subject: You have (1) new ecard! To: firstname.lastname@example.org Content-Type: text/plain; charset=UTF-8 X-Mailer: Opera/6.05 (Windows 2000; U) [fi] Click here to read it now! http://bit.ly/TMCHTA
To clarify: The above is an actual email that was sent to email@example.com even though the To header shows an sbcglobal.net address.
Perhaps if I understand how the spammers are doing this I can prevent it on my server. If it matters, my server is running SmarterMail 10.x.